Fiber-filled plastic compositions are widely used for making floor and wall tile, as well as for many other uses where the toughness which is imparted by fiber reinforcement is desired. In flexible, fiber reinforced plastic compositions, asbestos fibers have been commonly used, and continue to be used because of their many advantages, despite the major disadvantage that asbestos fibers are carcinogenic. Thus, the manufacture of plastic formulations containing asbestos presents difficult safety problems for the manufacturer.
Accordingly, it would be desirable to substitute the asbestos fibers in flexible plastic tile formulations and the like with another fiber, for example, natural or synthetic organic fibers such as polyester (Dacron) fibers, cellulosic fibers etc. Organic fibers are frequently preferred to inorganic fibers because their molecular chains can be broken or modified much more easily than the chains of inorganic fibers such as glass. Also, most organic fibers are of relatively low density as compared with inorganic fibers and accordingly offer significant savings in weight. However, the use of low density organic fibers on a commercial basis in plastic formulations has proven to be difficult, because the fibers have hitherto not dispersed easily throughout the plastic formulations during mixing. Accordingly, the finished products do not exhibit the desirable physical characteristics that one might expect from a fiber-reinforced plastic formulation. For example, the prior art finished products tend to exhibit insufficient tack, and thus do not adhere well to rollers for processing into sheet form.
In British Pat. No. 1,331,788, it is proposed to mix organic fibers into a plastic formulation for tile or the like, along with ground limestone particles (calcium carbonate) which generally range in particle size between 20 mesh and 200 mesh, to improve the structural properties of the tile such as abrasion resistance and hardness. However, the dispersion problem of organic fibers remains when ground limestone of this particle size is used, even when minor fractions of the limestone filler are smaller than 200 mesh. U.S. Pat. No. 3,904,579 proposes non-asbestos tile formulations which preferably do not contain any fibers. U.S. Pat. No. 3,931,094 and U.S. Pat. No. 3,336,259 disclose filled resin systems including inorganic fibers and which are suitable for making extruded products.